1. Field of the Invention
The present invention relates to an inertia drive engine starter and, more specifically, to an inertia drive engine starter having a slide output shaft provided with helical splines, and a splined sleeve provided with splines engaging the splines of the slide output shaft to shift the slide output shaft axially by the torque of the slide output shaft when the slide output shaft is rotated.
2. Description of the Prior Art
An inertia drive engine starter of such a type is disclosed in Japanese Patent Provisional Publication No. 56-107957. As shown in FIG. 2, this known inertia drive engine starter (hereinafter, referred to simply as "engine starter") is provided with an overrunning clutch 4 and a pinion 5, which are mounted axially slidably on the outer portion 3 of the armature shaft 2 of an electric motor 1. Internal helical splines formed in the inner surface of the boss of the outer race 4a of the overrunning clutch 4 are in mesh with helical splines 6 formed in the outer portion 3 of the armature shaft 2. The pinion 5 is formed integrally with the inner race 4b of the overrunning clutch 4. The inner race 4b and the pinion 5 are fastened to a sleeve bearing 7 axially slidably put on the armature shaft 2 in the outer portion 3. The armature shaft 2 is supported at its extremity in a bearing 14 fitted in a front end plate 15. Also shown in FIG. 2 are the ring gear 8 of the engine, a stopper 9 fixed to the extremity of the outer portion 3 of the armature shaft 2, a return spring 10 mounted between the pinion 5 and the stopper 9 on the outer portion 3, and a feed terminal M through which power is supplied to the electric motor 1.
Referring to FIG. 3, in operation, the starter switch 11 of the vehicle is closed to supply current from a battery 12 to the switch coil 13a of an electromagnetic switch, and then the plunger 13b of the electromagnetic switch 13 is attracted to bring a moving contact into contact with stationary contacts 13d and 13e, so that a normally open contact consisting of stationary contacts 13d and 13e is closed. Consequently, the battery 12 supplies current through the feed terminal M of the electric motor 1 to the field coil 1a and the coil of the armature 1b of the electric motor 1 to rotate the armature 1b. Then, the overrunning clutch 4 and the pinion 5 combined with the overrunning clutch 4 are caused to slide to the front (to the right as viewed in FIG. 2) against the resilience of the return spring 10 by the agency of the thrust of the helical splines 6 of the outer end portion 3 acting on the helical splines of the inner race 4b of the overrunning clutch 4 and the inertia of the overrunning clutch 4, so that the pinion 5 and the ring gear 8 are engaged to start the engine. When the starter switch 11 is opened, the moving contact 13c is separated from the stationary contacts 13d and 13e by a return spring, not shown, to stop supplying current to the electric motor 1, so that the pinion 5 is returned together with the overrunning clutch 4 to its initial position as shown in FIG. 2 by the return spring 10.
The extremity of the outer end portion 3 of the armature shaft 2 of the known inertia drive engine starter thus constructed extends to the front beyond the pinion 5, and the stopper 9 is fixed to the extremity of the outer end portion 3. Therefore, it is very difficult to mount the inertia drive engine starter on the engine because the extermity of the outer end portion 3 and the stopper 9 interfere with the ring gear 8 and, in some cases, the ring gear 8 is damaged by the extremity of the outer end portion 3 of the armature shaft 2 and/or the stopper 9. Furthermore, the extremity of the outer end portion extending beyond the pinion 5 and the stopper 9 attached to the extremity of the outer end portion 3 requires a space for receiving the same, which places restrictions on the design of the engine. Accordingly, improvement has been desired to solve those problems in the conventional inertia drive engine starter.